Manufacture of chlorofluorocarbons



hired; Sttcs Patent MANUFACTURE 8F CEELQRUFLUOROCAREONS Cyril Woolf, Morristown, N. 3., assignor to Allied Chemicall Dye Corporation, New York, N. 1., a corpora tion of New York No Drawing. Application .lune 21, B54, Serial No. 433,361

This invention relates to manufacture of l,l,2,2-tetrachloro-1,2-difluoroethane, i. e. symmetrical tetrachlorodifiuoroethane, CClaFCClaF, useful principally as a chemical intermediate, and particularly as an intermediate for manufacture of CClF=CClF monomer.

Heretotore, catalytic reactions of anhydrous HF with C2Cl4 and elemental chlorine, or hexachloroethane, or CzClsF in the gas phase have resulted in the formation of mixtures of CClzFCClzF and CChCCl-Fz, with the asymmetric CClsCClFz predominating. Prior art fluorinations of e. g. hexachloroethan by Swarts-type procedures have the disadvantage of forming a CClzFCClaF co-ntain-- ing product which can be purified only with diiliculties which are in addition to the usual difficulties encountered in SWarts-type procedures because of the presence of antimony haldies. CClzFCClzF has a boiling point of about 92.8 C. and a melting point of about 24.7 C., while CClsCClFz has a boiling point of about 91 C. and a melting point of about 406 C. In view of the close boiling points and the not too widely spread melting points of these two materials, from a practical viewpoint, the prior art difficulties attendant upon production of substantially pure CClzFCClzF are self-evident.

A major object of the present invention lies in the provision of gas phase catalytic processes for making CClzFCClF substantially free of CClsCClFs. Another object is provision of processes for making CClsCClFzfree CClzFCClzF from principally CCl2=CCl2, a relatively low cost and readily available starting material, by easily controllable gas phase catalytic operations which function in such a way as to effect production of CClzFCClzF without the formation of any appreciable amount of unwanted CClsCClFz, and without the disadvantages which are inherently present in prior art methods.

The invention comprises the discovery of the properties of a zirconium tetrafiuoride-activated carbon mass with respect to catalytic promotion of the reactions such as those subsequently disclosed. It has been found that the herein described zirconium tetrafiuoride-activated carbon material catalyzes the subject reactions in such a way as to substantially exclude formation of CClsCClFz and to produce CClzFCClzF substantially free of the isomer.

These catalytic materials may be made easily for example by impregnating activated carbon, of say 4-14 mesh size granulation, with an aqueous solution of a zirconium salt, such as zirconyl chloride ZrOClz, and drying at 125-200 C. in an inert gas stream such as nitrogen. Then the material is gassed with HP to convert the zirconium to DB1, temperatures being maintained above 125 C. and preferably at about ISO-200 C. Water and HCl formed during the reaction pass off in the vapor state. The presence in the reactor of Water or other solvent in liquid form is undesirable in order to avoid dissolving out zirconium salt from the impregnated carbon. Gassing with HF is continued until tail gases of the HF gassing operation indicate that evolution of HCl and water has ceased.

Patented Aug. 2, 1955 In general, raw material serving as the source of zirconium may be any zirconium salt which is soluble in vaporizable solvent and which reacts with HP to form ZrFr and a by-product vaporizing at the temperature of HF gassing. Thus, materials such as ZrOClz, ZrO(NOs)2, and ZrGCOs, ZrG(OH.)2 and also anhydrous ZICM may be used. While aqueous hydrochloric acid and water are the more desirable solvents, other suitable solvents may be employed. For example, a catalyst containing Weight parts of ZrFr per parts of Columbia 66 carbon may be made by dissolving 28 grams of substantially anhydrous ZrCl4 in 200 cc. of 10% hydrochloric acid, adding the liquid to 100 grams of the carbon, evaporating to dryness, transferring the impregnated carbon into a tubular nickel reactor heated by electric furnace, and passing preferably anhydrous HF into the impregnated carbon maintained at about -200 C. until evolution of Water and HCl ceases. As another illustration, 100 grams of activated carbon may be dried in nitrogen at about 300 C., and refluxed with 70 cc. of acetic anhydride and 180 cc. glacial acetic acid. Then anhydrous ZrClr (70 grams) may be added, and acetyl chloride distilled olf. Residual acetic acid may be removed by distillation at 20 mm. Hg pressure. The product containing zirconium tetra-acetate may then be gassed with HP at about 200 C. until evolution of acetic acid ceases.

In making the catalyst, any of the commercially available activated carbons may be employed, e. g. Columbia 66 carbon, Columbia SW carbon, or Darco carbon. If desirable, the activated carbon may be treated preliminarily to remove any silica by leaching with aqueous HF, water washing, and drying. The relative quantities of activated carbon and e. g. zirconyl chloride initially em: ployed may be such as to form an ultimate zirconium tetrafluoride-activated carbon mass which contains desirably a major quantity by weight of activated carbon and a minor quantity by weight of ZrFi. On the other hand, amounts of zirconium salt and activated carbon may be such as to form a final zirconium tetrafluoride-activated carbon catalyst containing as little as about 5% by weight of ZrFr. The catalyst preferably employed in practice of the invention may be considered as a zirconium tetrafluoride on activated carbon mass containing about 540% by weight of ZrF4.

While no attempt is made to summarize and explain the mechanisms of intermediate reactions taking place in practice of the invention, when using CCl2=CCl2, clemental chlorine and anhydrous HF as raw materials, the net result under the operating conditions specified, ap pears to be Reaction zone temperatures are maintained at or above the level at which fluorination of the CClz=CCl2 organic starting material begins to take place in the presence of gaseous HF and free chlorine. Reaction takes hold at temperature as low as about 300 C., but commercially significant reaction appears to require temperature of about 375 C. and above. No particular advantages have been noted when temperatures are above 600 C. On the other hand, overall best results appear obtainable at temperatures below about 500 C. Hence, in general prac tice of the invention, preferred temperatures are in the approximate range of 375-500" C.

Mol ratios of CClz=CCla to HP and to elemental chlorine are theoretically 1:2 and 1:1 respectively. In general, the quantities of HF and C12 utilized are sutficient to provide for formation of chlorofluorocarbon reaction product containing a worthwhile quantity of CClzFCClaF. Preferably, amounts of HF and C12 should not greatly exceed theoretical requirements, and, depending upon particular operating conditions, quantities. of HF may vary from one to 2.6 mols per mol of C2Cl4, minimization of the amount of HF employed being preferred to reduce thesquantity of tri and tetrafluorinated products formed. To facilitate good utilization of chlorine, amounts of the latter may vary from 0.75 to 1.25 mols per mol of C2Cl4.

Time of contact of C2Cl4 starting material with the described catalyst may be varied substantially without noticeable sacrifice of efiiciency of operation. However, if contact time is excessive, i. e. low space velocities, the capacity of the reactor is low thereby causing economic disadvantages in the operation. On the other hand, if contact time is too short, the reaction of starting material to form desired product may be incomplete thereby entailing possible high cost of recovering and recycling unreacted material to subsequent operation. In all embodiments of the invention, contact time should be suiiicient to'efiect fluorinating reaction of a commercially notable amount of the particular starting material. Contact time may lie in the range of about 2 to 25 seconds, preferably about 3 to 12 seconds. In a particular operation, optimum contact time, within the values indicated is dependent upon variables such as scale of operation, quantity of catalyst in the reactor, and specific apparatus employed and may be best determined by a test run. Atmospheric pressure operation is preferred, but the reaction may, if desired, be carried out at superatmospheric or subatmospheric pressure, the choice of pressure being largely one of convenience. If desired, CzCle or CzClsF may be used as starting material in place of C2Cl4 and chlorine. In the case of CzCls, temperatures, quantity of HF employed and contact times may be substantially as indicated when C2Cl4 is employed as organic starting material. If C2Cl5F is utilized, temperatures and contact times may be about as indicated, and quantity of HF may vary from about 0.75 to 1.25 mols per mol of CzClsF.

Any suitable chamber or reactor tube constructed of inert material may be employed for carrying out the reaction provided the reaction zone aiforded is of sufiicient length and cross-sectional area to accommodate an adequate amount of catalyst and afford sufficient space for passage of the gas mixture at an economical rate of How. Material such as nickel, graphite, Inconel or other substances resistant to HF are suitable for use as reactor tube. Externally disposed conventional means may be employed to furnish heating or cooling needed to maintain the desired catalyst bed temperatures. 7 Since the overall reaction is exothermid to some extent, in large scale work the reaction is carried out preferably in tubular reactors which may be externally cooled.

Reaction products may be recovered by conventional procedure. The temperature of the gas stream exiting the reactor may be lowered in an initial cooler to e. g. to 60 C., the gas stream then scrubbed with water to condense high boiling chlorofluorocarbons including the principal organic product and to remove HF and HCl from the gas stream, passed thru aqueous caustic solution to remove chlorine and residual small amounts of HCl and HF, then passed over calcium chloride or other drying agent. If recovery of low boilers is desired, the gas stream may be run thru a cold trap maintained at temperatures substantially below the boiling point of the lowest boiling material present, e. g. by indirect cooling of the gas in a bath of acetone and carbon dioxide ice. High boiling chlorofluorocarbons condensed in the water scrubber solution are separated therefrom, and the organic condensates together with those from the initial gas cooler may be combined with the condensate of the cold trap. The resulting composite liquor comprising reaction products and unreacted starting material, may be fractionally distilled to separate components to the extent desired.

The following are examples of practice of the invention, parts and percentages being by weight unless otherwise indicated.

Example 1.150 cc. of catalyst, consisting of 81% Columbia carbon 6G and 19% ZrF4, about 4 x 14 mesh,

were charged into a one inch 1. D. tubular nickel reactor maintained at a constant temperature by external electric heat automatically controlled by a potentiometric device actuated by a thermocouple. The reactor was heated for a length of about 36 inches, the catalyst being centrally disposed to allow about 12 inches for preheating of reactants. As preferred, to purify the incoming tetrachloroethylene, the latter was passed separately thru cc. of Columbia 6G carbon, 8 X 14 mesh maintained at about 318 C. before entering the reactor. Thereafter the pretreated tetrachloroethylene was mixed with HF and chlorine and the mixture passed into the reactor. During reaction, temperature was in the range of about 450 C. to 473 C., the latter being the maximum internal temperature. Flow rates of reactants were as follows: HF, 1.25 mols/hr.; C2Cl4, 0.60 rnol/hr.; and chlorine, 0.623 mol/hr. Conversions (per cent by weight reacted) of the reactants were about HP, 60%; C2Cl4, 72%, and chlorine, 69%. Contact time was about 4 seconds. The gas mixture exiting the reactor was handled by conventional methods, and the chlorofluorocarbon products recovered and quantities thereof were as follows: CClzFCClzF, B. P. 928 C., 0.253 mol/hr.; CzFCls, B. P. 137.9 C., 0.144 mol/hr., and CCI2FCC1F2, B. P. 47.7 C., 0.34 mol/hr. The CaClsF may be recycled.

Example 2.-In this example, the same apparatus and catalyst as described in Example 1 were employed. Average internal temperature throughout the run was about 402 C. Flow rates of incoming reactants were HF, 1.18 mols/hr.; C12, 0.645 mol/hr.; C2Cl4, 0.57 moi/hr. Conversions were as follows: HF, 43%; C12, 68%; C2Cl4, 81.4%. Contact time was about 4 seconds. As in Example 1, the exit of reactor was handled by conventional methods, and the products and quantities recovered were as follows: CClzFCClzF, 0.118 mol/hr.; CzFCls, 0.327 mol/hr.; and CClzFCClFz, 0.003 mol/hr.

Example 3.A 1.5 inch 1. D. tubular nickel reactor was filled with 1000 cc. of catalyst consisting of 8 x 14 mesh'Columbia 6G carbon containing about 7.4% of ZrFi. During reaction, internal temperature was main tained at about 475 C. Flow rates of reactants were C2Cl4, 1.13 mols/hr.; chlorine, 1.13 mols/hr.; and HF, 2.80 mols/hr. Conversions of HF, C2Cl4 and chlorine were respectively 70.6%, 68.7% and 68.7%. Contact time was about 12 seconds. The reactor exit gas was handled conventionally, and products and quantities thereof recovered were as follows: CClzFCClzF, 0.35 mol/hr.; CzFCls, 0.24 mol/hr.; CClFzCClzF, 0.09 mol/hr. Minor quantities of CClFzCClFz and CCl2F2 were recovered.

Examination, by melting point and infra red techniques, of the CClzFCClaF products of each of the following examples failed to detect the presence of CClsCClFz. Hence, such products were substantially free of CClsCClFz.

I claim:

1. The process for fluorinating CClz CClz to form CClsFCClzF which comprises introducing a gas phase mixture comprising CClz CClz, substantially anhydrous HF and free chlorine into a reaction Zone, the amount of HF and free chlorine being sufiicient to ultimately form a substantial quantity of CClzFCClzF, and heating said mixture in said zone at temperature in the approximate range of 300600 C., while in the presence of zirconium tetrafluoride-activated carbon cata lyst, for a time sulficient to cause fiuorinating reaction of a substantial quantity of CClz CClz and etfect formation of a gaseous chlorofiuorocarbon reaction product comprising a substantial quantity of CClzFCClzF.

Z. The process of claim 1 in which there is recovered CClsFCClzF substantially free of CClsCClF2.

3. The process of claim 1 in which temperature is in the approximate range of 375500 C.

4. The process for fluorinating CCI2=CC12 to form CClzFCClzF which comprises introducing a gas phase mixture comprising CCl2=CCl2, substantially anhydrous HF and free chlorine into a reaction zone, the amount of HF and free chlorine being sufficient to ultimately form a substantial quantity of CClzFCClzF, and heating said mixture in said zone at temperature in the approximate range of 300600 C., while in the presence of zirconium tetrafluoride-activated carbon catalyst.

5. The process for making CClzFCClzF which com prises introducing into a reaction zone a gas phase mixture of the group consisting of 1) CClz=CClz, substantially anhydrous HF and free chlorine, (2) CzCls and substantially anhydrous HF, and (3) C2CI5F and substantially anhydrous HF; the amount of HF and chlorine available being sufiicient to ultimately form a substantial quantity of CClzFCClzF, and heating said mixture in said zone at temperature in the approximate range of 300600 C., while in the presence of zirconium tetrafluoride-activated carbon catalyst, for a time sufficient to cause fluorinating reaction and effect formation of a gaseous chlorofluorocarbon reaction product comprising a substantial quantity of CClzFCClzF.

6. The process of claim 5 in which temperature is in the approximate range of 375-500 C.

7. The process of claim 5 in which there is recovered CClzFCClzF substantially free of CClsCClFa.

8. The process for fiuorinating CCl2=CCl2 to form CClz'FCClzF which comprises introducing a gas phase mixture comprising CCl2=CCl2, substantially anhydrous HF and free chlorine into a reaction zone, the amount of HF and free chlorine being suflicient to ultimately form a substantial quantity of CClzFCClzlF', heating said mixture in said zone at temperature in the approximate range of 37 5-500 C., while in the presence of a zirconium tetrafiuoride on activated carbon catalyst, for a time sufficient to cause fluorinating reaction of substantial quantity of CCl2=CClz and effect formation of a gaseous chlorofluorocarbon reaction product comprising substantial quantity of CClzFCClzF, and recovering CClzFCClzF substantially free of CClsCClFz.

9. The process of claim 8 in which there are introduced into the reaction zone C12 and C2C14 in mol ratio in the approximate range of 0.75 :11.25:l, and HF and C2Cl4 in mol ratio in the approximate range of 1:1-2.6: 1.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE PROCESS OF FLUORINATING CCL2=CCL2 TO FORM CCL2FCCL2F WHICH COMPRISES INTRODUCING A GAS PHASE MIXTURE COMPRISING CCL2=CCL2, SUBSTANTIALLY ANHYDROUS HF AND FREE CHLORINE INTO A REACTION ZONE, THE AMOUNT OF HF AND FREE CHLORINE BEING SUFFICIENT TO UNTIMATELY FROM A SUBSTANTIAL QUANTITY OF CCL2CCL2F, AND HEATING SAID MIXTURE IN SAID ZONE AT TEMPERATURE IN THE APPROXIMATE RANGE OF 300-600* C., WHILE IN THE PRESENCE OF ZIRCONIUM TETRAFLUORINATING-ACTIVATED CARBON CATALYST, FOR A TIME SUFFICIENT TO CAUSE FLUORINATING REACTION OF A SUBSTANTIAL QUANTITY OF CCL2=CCL2 AND EFFECT FORMATION OF A GASEOUS CHLOROFLUOROCARBON REACTION PRODUCT COMPRISING A SUBSTANTIAL QUANTITY OF CCL2FCCL2F. 